Method of improving retention of fillers in paper making with acrylamidediallylamine copolymer



United States Patent METHOD OF IMPROVENG RETENTION 0F FILL- ERS IN PAPER MAKTNG WITH ACRYLAMIDE- DIALLYLAMINE CQPGLYMER Glenn A. Goldsmith, Berwyn, Ill., assignor to Nalco Chemical Company, Chicago, 131., a corporation of Delaware No Drawin Filed Jan. 8, 1963, Ser. No. 249,998

8 Claims. (Cl. 162-163) This invention, in general, relates to additives useful in the processing of paper. More particularly, this invention is concerned with polymeric compositions which show activity in retention of fillers and fiber fines in paper manufacture.

Paper is manufactured for the most part from wood pulp. A small amount of high grade paper is manufactured from rag pulp. There are five different kinds of wood pulp: mechanical pulp (ground wood), semi-chemical pulp, sufite pulp, sulfate or kraft pulp, and soda pulp. The first is prepared by purely mechanical means, the second by a combination of mechanical and chemical, and the other three by chemical means. The mechanical pulp contains substantially all of the wood except the bark and that lost during storage and transportation. Semi-chemical pulps are partially free of lignin. Chemical pulps, however, are essentially cellulose, the unwanted lignin and other non-cellulosic components of the wood having been dissolved away by the cooking and bleaching treatment. Because of this, chemical pulps are much superior to mechanical and semi-chemical pulps for fine paper making. However, because of the special processing required, they are too expensive to serve as the main source of fiber for the cheaper grades of papers such as newsprint.

If the pulp fibers were the only constituents of a paper sheet, the usefulness of the paper would be very restricted because the sheet would be soft, have a yellowish color, and could not be written or printed upon with ink successfully. If the sheet were thin, it would be transparent to matter printed upon the opposite side. t is necessary, then, to add other substances, such as sizing, coloring agents, and fillers, to the cellulosic fibers to produce paper suited to its many uses.

Many papers, except the absorbent types, filter papers, and most packaging papers, must have a finely ground filler added to them, the purpose of which is to occupy the spaces between the fibers-thus giving a smooth surface, a more brilliant whiteness, improved printability and improved opacity, The fillers are inorganic substances and may be either naturally occurring materials such as talc, agalite, pearl filler, barytes and certain clays such as china clay or artificial fillers such as suitably precipitated calcium carbonate, crown filler (pearl hardening); blanc fixe', and titanium dioxide pigments. Sizing is added to the paper, other than absorbent papers and filter paper, to impart resistance to penetration by liquids. Common sizing agents added to the pulp before it is formed into a sheet are wax emulsions or soaps made by the saponification of rosin with alkali. The sizes are precipitated with alum.

Pulp stock isprepared for formation into paper by two general processes, beating and refining. Mills use either one or the other alone or both together. The most generally used type of heater is that known as the Hollander. Beating the fibers makes the paper stronger, more uniform, more dense, and less porous. It is in the beater that fillers, coloring agents and sizing may be added. The standard practice in making the finer grades of paper, is to follow the heaters with the refiners, the latter being continuous machines.

ice

While the usual practice is to add filler, sizing and color to the beaters, they may be added prior to the Jordan or to a combination of points in the system or subsequent to the beating operation but prior to the refining step, as for example, prior to beating. The order in which the materials are added to the heaters may vary with different mills. Generally,- however, the filler is first added to the blended pulp, and after sufficient beating, the sizing and the coloring are added. In some instances, all or part of the sizing and the coloring are added. In some instances, all or part of the sizing is surface applied to the formed, dried sheet, using animal glues, starches, or gelatin as the sizing. Again, alum is most generally added to thebeater, but in some mills, this practice is varied, and the pulp may be treated with this chemical during the refining step or even later in the paper processing scheme.

The machines used for the actual formation of the paper sheet are of two general types, the Fourdrinier machine and the cylinder machine. The basic principles of operation are essentially the same for both machines. The sheet is formed on a traveling bronze screen or cylinder, dewatered under rollers, dried by heated rollers and finished by calender rolls. In the Fourdrinier machine, the stock of the foregoing operations is sent to the headbox from which it flows onto a moving, endless bronze wire screen. The pulp fibers remain on the screen while a greater portion of the water, containing unretained fiber fines and unretained filler, drains through. As the Fourdrinier wire moves along, it has a sidewise shaking motion whch serves to orient some of the fibers and give better felting action and more strength to the sheet. While still on the Fourdrinier wire, the paper passes over suction boxes to remove water and under a dandy roll which smooths the top of the sheet. In the cylinder machine, there are several parallel vats into which similar or dissimilar dilute paper stocks are charged. A wire-covered rotating cylinder rotates in each vat. The paper stock is deposited on the turning screen as the water inside the cylinder is removed. As' the cylinder revolves further, the paper stock reaches a point where the wet layer comes in contact with and adheres to the moving felt. This felt and paper, after removal of some water, come into contact with the top of the next cylinder andpick up another layer of wet paper. Thus, a composite wet sheet or board is built up and passes through press rolls and onto the drying and smoothing rolls. 7

In an attempt to improve filler and fines retention in the paper manufacturing operation several attempts have been made to incorporate chemical additives with the paper stock before it reaches either the cylinder vat or the Fourdrinier wire. These additives, for the most part, have not been entirely satisfactory from several operational points of view. One of the chief drawbacks of. most chemicals used to improve a fiber and fine retention in the manufacture of paper is that they must possess certain characteristics and properties which are extremely difiicult to achieve in any particular chemical. For instance, the particular chemical used should not be afiected by other additives normally used in the paper processing operations such as rosin size, alum, sodium aluminate, starch, clays, and the like. Also important for a particular additive to be effective for improving fiber and fine retention is that it must not be affected by variations in pH. Similarly, the ideal additive chemical should not be affected by a particular electro-kinetic charge on the cellulose fibers and fines. The use of a chemical must, of course, be such that it does not have any adverse effects on the finished sheet and it should be relatively safe to handle.

In addition to possessing the above desirable characteristics an additive for improving filler and fines retention must be capable of acting both upon the filler and fines in the system to efficiently cause such materials to be retained in the finished sheet rather than with one being I preferentially acted upon by the additive. Another important characteristic that must be capable of operating on a large variety of stocks.

Also of importance in the selection of-fines and'filler retention agent is that it must not affect dyestuffs which are frequently used as coloring agents for various types of paper stocks.- It also must not interfere with the beneficial effects imparted to paper stocks by coatings which are frequently placed on different types of paper during its manufacture.

Many prior art filler and fiber fines retention aids fail to achieve the above desired objects. tain of these known retention additives cannot be .em

ployed in effective combinations with various fillers or other paper additives. Oftentirnes efficiency is low ,except when gross uneconomical amounts are added Ad-. verseeffects upon the finished paper product are noted when these retention aids cause poor dispersibility of the system additives with resultant localized non-uniform areas. trapage on the top sideof the fiber material.

' It, therefore, becomes an object of the invention to provide a new and improved method for improving filler and fines-retention in the manufacture of paper. .by addi tion of water-soluble polymeric substances during paper processing.

'A, further object is-to provide chemical agents for im. proving filler and fines retention which are eifectiveat low economical dosages, will not interfere with otheraddie tives and substances used in the make-up and manufacture of the paper, and which have no adverse effectson the chemical and physical characteristics of the finished sheet.

Yet another object of the invention is to provide watersoluble polymeric retention additives which when used in combination with alum give especially improved retention effects.

An important object of the invention is to provide chemical additives for improving filler and fine retention in manufactured paper which will operate on a wide variety of paper stocks, are fairly safe to handle and will impart to the finished sheet certain anddesirable char-.

acteristics which have not heretofore been available vwhen prior attempts have been made to use other chemicalsas fines and filler retention .aids.

A special object of the invention is to vprovide versatile high molecular weight completely water-soluble .copolymers for use as retention aids which have the additional property of ability to increase drainage properties of the formed paper pulp sheet prior to final processing. via dry- 7 ing. The copolymers causeleflieient drainage of. water from the formed fiber network which has been placed on a foraminous. forming surface.

In addition, cer- Lastly, many additives fail by promoting filler.

The first essential monomeric starting reactant is acryl amide. This monomer is. easily obtained by well-known commercial processes such as partial hydroly'sisof acrylonitrile. While the amounts of acrylamide in parts by weight which may be employed may he varied over a wide range, for'best results, it has; been determined that;

preferred high molecular weight solid materials maybe prepared through use of 50-95 parts by weight of acryl-I amide starting material. per 100 parts by weight of copoly- 60 to 90 parts by weight per :l00parts by weightof co-' polymer. Copolymers synthesized byuseof acrylamide, I in the above recited ranges in combination 'with mono-' meric allylamines have exceptional ability retaining in- In accordance with the invention it has been discovered that water-soluble copolymeric materials comprising polymerized acrylamide and an allylamine or salt thereof have.

excellent activity in promoting filler and fiber fine-s retention in papermaking processes. The copolymers show a retention activity even at addition levels as low as 0.01

pound per ton based on the .weight of dry fiber, have unusually good water solubility, and may be used as retention aids for all fiber furnishes including both bleached, and unbleached primary or virgin chemical pulps, mechan1 cal pulps, and secondary fibers, that is, fibers previously;

dependent upon the amountvof each monomer employed.-

The exact molecular configuration, of course, cannot be determined, but is rather considered a statistical aver.-

organic fillers and fiber fines upon a pulp network. Thus,

effective utilization of the above filler additives andpaper stock is achieved, and the residual White water which re-:'

mains after the sheethas been drainedand formed will have low amounts ofsuspendedsolids.

Preferably, when R is a lower alkyl" radical it containsless than about 4 carbon atoms.

from 10 to 40 parts of the diallyl amine monomer. In

the most preferred embodiment then, the; copolymer con-.

tains from about 60 to; about parts of acrylamide and from about 10 to about 40 parts of the cationic allylic monomer. Representative allylic compounds which may be copolymerized with acrylamide include diallylamine,

dimethallyl-amine, ,diallylmethylamine, dimethallyethylg amine, etc. .As already mentioned, for eifcctiv'e resultsany of=the above copolymers must be water-solublei in order to act as, suitable .filler and fines retention" aids,- and gen erally have a relatively high molecularweight of at leas 10,000'and preferably above 50,000..

In order to) prepare the :above allylic-acrylamide copolymers it is only necessary to mixthe ingredients in the desired proportions and polymerize them by known techniques such :as bulk, solution; emulsion, suspensions means etc.v The catalyst initiatormay be any. free radical However, it has been foundtha't oneparticularly preferred polymerization synthesis insuch a producing agent.

case is a solution polymerization wherein a redox catalyst system comprising -a catalystinitiator and reducing agent is employed in conjunction with a metal activator. Using this scheme, relatively high molecular weight water-; soluble .viscous materials are produced which have excel lent activity intpromoting retention of paper pulpfines and fillers. t

In a preferred embodiment involving a solution-polymerization the allylic amine isfirst reacted with mineral or organic acidsisuch as hydrochloric, sulfuric, phosphoric,

The :mostpreferred range of acrylamide used iSr In many cases, subsequent processes-for recovery of the suspended solids; are not needed, and the .white :watermay be directly re-. used in;the pulp making andprocessing, If recovery is; necessary, the task is made much simpler by the reduc-v The ;above amine prefer-; ably makes up 5-50 parts per parts ,by weight of, the

copolymeric compositions which more preferably contain nitric, formic, acetic, etc., to form salts thereof. To the salt, normally formed in an aqueous solution, is then added acrylamide monomer. The scheme of addition, however, is immaterial. The pH of the monomer mixture generally ranges from 4 to 6 at this stage in the reaction. To the above is then added the catalyst system to initiate the reaction. The polymerization is generally started at ambient temperatures.

During the reaction itself, heat is given off by virtue of the exothermic nature of the polymerization. Temperature rises of 50-100 F. have been noted. Generally, the bulk of the polymerization reaction occurs between 100 and 200 F. Agitation is usually employed during the mixing of monomer ingredients and polymerization step itself.

The reaction mixture then is compounded of aqueous solutions containing about 5 to 80% by weight of monomers, 20% to 95% of water, and 0.001% to about 0.2% of catalyst based on the total weight of reaction mixture. Preferably 0.01 to 0.1% of catalyst is employed. While a redox system of catalyst is preferred, the invention may also include sole use of conventional peroxide oxidizing agents such as potassium persulfate, hydrogen peroxide, and ammonium persulfate.

As noted above, in the preferred embodiment the reaction is initiated by a redox catalytic system additionally containing a metal ion. In 'a redox system, the catalyst is activated by means of a reducing agent which produces free radicals without the use of heat. One of these reducing agents most commonly used is sodium metabisulfite. Other reducing agents include water-soluble thiosulfates and bisulfites, hydrosulfites and reducing salts such as the sulfates of metals which are capable of existing in more than one valence state. These metals include cobalt, iron, nickel, and copper. The use of a redox initiator system has several advantages, the most important of which is efficient polymerization at lower temperatures. It is therefore not required to decompose the catalyst. The selection of catalyst and reducing agent, should a redox catalyst be used, and the selection of metal activators, for use in the process may be varied according to the choice of the experimenter. Conventional catalysts such aspotassium persulfate, ammonium persulfate, etc., used in conjunction with the above reducing agents and metal activators such as ferrous ammonium sulfate work very satisfactory. Use of other metal ions than ferrous ion whose valence state is capable of being varied such as cobalt, iron, nickel, and copper also improve the polymerization scheme. In the most preferred initiator system, ferrous ammonium sulfate, ammonium persulfate, and sodium metabisulfite are employed and when added to the monomer mixture give excellent polymerization products in a minimum of time. In particular, use of ferrous ion obviates the need for nitrogen sparging, which for other systems is normally required to give the most acceptable product. One preferred initiator system contains 50-100 p.p.m. of ferrous ion as ferrous ammonium sulfate, 100 p.p.m. sodium metabisulfite and 100 p.p.m. ammonium persulfate. When a redox catalyst system is employed in conjunction with a metal ion, the concentration of each may range from 0.001 to 0.2% and preferably from 0.01 to 0.1% based on the weight of the reaction mixture.

The following examples are illustrative of representative types of allylamine-acrylamide .copolymers and various techniques employed in producing same according to the solution method generally outlined above.

Example I A monomer solution containing 125 grams of diallylamine was added to an open vessel equipped with an agitator. 125 grams of hydrochloric acid (approximately 37% concentration by weight) was added to the diallylamine solution in order to form the hydrochloride salt thereof. The pH of this solution was approximately 4.5. To the diallyl salt solution was then added 375 grams of acrylamide, also made up in aqueous solution. The respective monomers were thoroughly mixed and suflicient catalyst initiator system, composed of ferrous ammonium sulfate, sodium metabisulfite, and ammonium persulfate, as 1% solutions, were added to give 6, 1, and 1 grams of these reagents respectively. The three reagents were prepared as solutions just prior to their use, since decomposition occurs to some extent in all three solutions. The water content of the reaction mix was adjusted to give a 20% monomer solution. The polymerization reaction proceeded exothermally, starting at ambient temperature (7095 R). During the course the reaction appeared to be complete, that is, when heat ceased to be evolved due to the reaction, the copolymer was then diluted to a 5% solution of active copolymer comprising polyacrylamide and polydiallylamine hydrochloride salt. In this example, the ratio of starting monomer acrylamide to starting monomer diallylamine was :25.

Example 11 A 3-neck flask, equipped with stirring device, thermometer, nitrogen sparger and heating mantle, was set up into which monomer solutions of acrylamide and diallylamine salt were introduced and then thoroughly mixed. Then a vacuum was applied along with heat which was in turn followed by nitrogen sparging. This step was carried out in order to rid the system, both solution and atmosphere above the solution, of air containing oxygen. The catalyst, consisting of a redox system of sodium metabisulfite and ammonium persulfate, was added with continued nitrogen sparging, and the solution was then allowed to polymerize. A 500 gram amount of 10% solution of active chemical prepared with an :15 ratio of acrylamide to diallylamine was produced.

Example III 25 pounds of diallylamine was added to 375 pounds of Chicago tap water and placed in a stainless steel reactor (Dopp Kettle). To this was added 25 pounds of a 37% concentration solution of hydrochloric acid producing the diallylamine salt. The pH of this solution at this time was 4.6. 75 pounds of acrylamide was then added to the salt solution and the temperature adjusted within the range of 7095 F. The initiator system, consisting of 126.3 grams of ferrous ammonium sulfate, 22.7 grams of sodium metabisulfite and 22.7 grams of ammonium persulfate, was added and the reaction allowed to proceed. 30 minutes after a peak temperature of F. was reached, 1,500 pounds of Chicago tap water was added to give a final product containing 5% active copolymer.

In order to produce copolymers of even higher molecular weight and correspondingly proportional excellent retention ability, the special polymerization technique discussed in commonly assigned application, Serial No. 132,562, filed August 21, 1961, may be employed. Broadly speaking, this technique involves preparation of the highly concentrated monomer solution, addition of an inert heat transfer solvent media, which may be re ferred to as an organic solvent, and subsequent polym erization effected at relatively low temperatures. The polymerization must be carried out under conditions of high agitation and in the presence of an anti-sticking agent, which acts to keep the formed polymer from agglomerating into an unusable mass. The monomers actually copolymerize in a separate stratum within the above system in the presence of a surface active compound acting as the anti-sticking agent. If conditions are followed closely, granules of relatively small size may be obtained which are easily ground into a free-flowing white soluble powder, and are immediately ready for use without further processing.

More specifically, an aqueous solution is prepared containing about 30% to about 80% by weight of monomers, 20% to 70% water, and 0.003% to about 0.2% based on the weight of monomer present of the polymerization 7 catalyst, such as potassium persulfate. The water solution is then added to 'or mixed with a water-insoluble, organic, heat transfer medium which preferably is capable of forming an azeotropic mixture with water. The above mixture should contain a minor amountof a surfaceactive agent which prevents the copolymer from sticking to the agitator or the walls of the vessels The temperature of the system is raised to a desired pointwand the mixture is kept inzmotion by means of an agitator;

Oxygen is removed from the system either by'purging With'an inert gas such as nitrogen or carbon dioxide, by applying a vacuum or by boiling the mixture. The pot lymerization is initiated as soon asthe oxygen is removed. If an emulsion has formed due to the presence of .the sur:. face-active agent, that emulsion breaks at the time polymerization starts and the polymerization is carried out in a separate layer. stantially surrounds the aqueous medium as therpolymerization takes place. continuously shear the polymer layer-into particles which vary indiameter, for example; from about 5 to about 2" and more often from about A to 1/25. 'In a pre-..

ferred process, the temperature of the. mixture is raised I The organic heat transfer medium sub- Vigorous agitation is employed to to its boiling point or maintained at the boiling point, in a 25. After the polymerizationis com- 1 with the particular organicheat transfer agent in ::the

mixture;

During the boiling off stage, the organic solvent pref.-= I erably is condensed and returned-to the mixturewhile Y the water is being trapped and removed. After from-60 to 100% of the water has been eliminated, the granules that have formed are separated from the solvent by filtration and are then Washed and air dried.

It has been found that benzene, toluene, xylene, and ethylene dichloride are especially suitable for use in the present process as well.as carbon 'tetrachloride, tetrachloroethylene, .and the like. Other comparable organic; compounds that form azeotropic mixtures of Water,- how- 1 ever, could be used without difliculty as long as they do not contain alcohol, aldehyde: or ketone groups which would cause undesirable sidereactions. The polymerization medium can also contain a non-azeotroping com-p ponent with boiling pointv above the distilling tempera: I

ture. The above materials may. be'termed organicsblvents. and are all water'insoluble, organic heat exchange. materials which are considered inert in the practice of the: invention. Theseorganic. substances serve as heat trans fer media or heat dissipators by suspension of the aque-' capacity; Materials such as Ethomid S-l5, O-15, and

HT-, which are ethylene oxide. condensates of. fatty acid amines, as well as Arlacel 80 and Span 80, which are sorbitan mono oleates, will serve adequatelyas anti-- sticking agents as will tsorbitan monostearate, sodium dodecyl Lbenzene sulfonate,. aluminum stearates, vand, aluminum oleates. Initially in'the process, the presence of thesurface active agent may cause the. formation of.

an emulsion. Itj is essential, however, that the emulsion break andform two separate andudistinct layers prior to the polymerization reaction. The amount of surface active agent which is added to the system can vary from about 0.5% to about 7% by weight based on the weight exothermic reaction has been completed, ltemperature of the mixture of the polymerization reaction is maintained at about 70 C. for -60 minutes.- At. this time, water. is then removed. as -an'azeotropici..distillate.-. Approxi- 7 8? of the. heat transfer medium, and .pr'eferablywill vary from about 2%'to,4%.

As was further pointed out above,v the. heat transfer The removal of dissolvedoxygen gas from'the reaction mixture isi also important. The removal. of the oxygen can be accomplished by (1). purging. the reaction mixture with an inert gas such as nitrogen or carbon dioxide, (2)

boiling the reaction mixture, and (3) applying a partial vacuum to the system; 'If aninerti gas isused to remove the oxygen; it is:best applied by passing the :gas through a disperser or sparger which is inserted beneath the'.sur-;

face of the reaction mixture;

, The -water contentof the copolyrners; that are produced by the. above method should range from-0 to about 28%.;

The preferred ,water content: range "is from about:5% to about 15%. If themoisture'content of the .polymer is about. 28%,.the granules tend to agglomen;

greater than.

ate.-

The following example illustrates. .how a typical copolymeric retention aid of the invention ,may 1 be suitably produced" by the :above high monomer: concentration method. 1

' Example IV To 108.0 grams of water are added 101.25 grams of acrylamide and I34.75.,grams. of diallylamine- .whi-ch had been previously reactedtwith sufficientconcentrated hydrochloric acid .to .form the salt thereof. The above-ingredients are mixed until complete ,solubilization'is .effected. The entire solution is gentlyfagitatedand mildly:

heated at a temperaturenot greater than .338". C; It is essential that the temperature not exceed the above limit since heating at a higher temperature would effect. polymerization prematurely..

flask then is purged with nitrogenat a rate of 960, cc.,/ min.

Afterylthe inert solvent ;and anti-sticking agent mixture is purged .sufliciently, the above monomeric solution is added to .the v1000.ce.;reactio'n flask. The system is putv under reduced vacuum (8 inches) and heatedto C. After this temperature is reached, thev vacuum is.shut;off

. and 4.8 grams of a. 1% aqueous. solution of Na S O5 -is the reaction temperature drops two=to.three degrees C.

The redox catalyst is completely, added, ithe vacuum is re-establishedat an 8" reading,=;and.the reaction mass is reheated .to 70 C. When, this. temperature. is again reached the .vacuum is shut off and. only nitrogen is introduced into 'thereactiommixture :for theidu'ration of the reaction timev Heating is appliedin aorder tomaintain the reactionimass :at. 70 C., until an exothernroc:

curs. At this time, .heat is discontinuedsand the-temperature drops of-itst own accord=to 681 C. Afterthe mately of the total water addedwasazeotroped off. Filtration fromthe organic solvent lefta white solid granular copolymeric product.

It is understood, ofqcourse, that the above discussed methods are only illustrativetof typical .preferred'prepa.

rations of the copolyrnerieretention aidsyof the--invention. Theinventionin its broader aspects, resides in use of such polymers-and is not dependentupon theparticu- 9 lar polymerization technique used. Also, the invention contemplates the use of both allylarnine and its salts as starting monomer materials.

EVALUATION OF THE INVENTION In order to determine the effectiveness of the copolymers of the invention, two procedures were devised. The first, known as the Phototester Method involved a measurement of the light absorption of a supernatant liquid remaining after settling of a dispersion of pulp and titania. A blank was run and then compared to samples in which the retention aids of the invention had been previously added. The difference between the percent absorption of the blank sample and the percent absorption of the treated sample gives them a Phototester number. This number is directly related to the ability of the sample tested to act as a retention aid, with retention activity directly proportional to the increase in the Phototester number. The higher the number, then, the greater the'retention activity. If, for example, a blank sample gives a 60% absorption and a treated sample a 40% absorption, the difference stated as an. absolute number is 20,which,then is the Phototester number.

More specifically, this Phototester method is as follows: Bleached sulfite pulp is beaten for 30 minutes and added to the proportioner of a Noble Wood Sheet Machine and the consistency adjusted to give a 0.21% fiber content. To this pulp slurry is added 75 mls. of TiO which had been previously slurried in water to give a suspension,

to give an addon of based on the fiber weight. After the titania has been thoroughly dispersed in the pulp for five minutes, 30 ml. of a 2.5% solution of alum is added to give a concentration of 2% alum, based on the fiber weight. The alum is added in order to standardize the system in meeting normal paper mill procedure. The pulp furnish is then removed from the proportioner to a porcelain lined pail and stirred for one hour. Before stirring, the pH had been adjusted as desired with a normal sulfuric acid solution. The pulp furnish, containing the titanium alum is then allowed to settle for one-half hour and the sample of the supernatant liquid is taken and tested in the Phototester machine for light absorbency. The figure obtained, then, corresponds to the percent absorbency of a blank, that is, a pulp treated with titania filler and alum in which no retention aid had been added.

In order to evaluate the retention activity of the polymers of the invention, a 125 ml. sample of pulp containing alum and titanium is added to a ounce jar. The retention aid is then added from a 0.02% solution and the entire mixture swirled briefly. 375 ml. of tap water is added, the jar is capped and inverted five times and allowed to stand for five minutes. The supernatant liquid is then removed and a Phototester measurement taken. In order to avoid aging of solutions which would result in a less meaningful determination, all of the above test solutions of titanium, alum and retention chemicals are freshly made each day. Also, the titanium suspension is never allowed to settle between the time it is made and the time it has been added to the pulp suspension.

The next test method for determining retention activity is known as the Ash Determination Method. In this method, titania and alum are added to the bleached sulfite pulp as outlined above in the Phototester method. The systemis then adjusted to any desired pH. If a blank run is desired, thepulp furnish is then transferred to the head box of a Noble and Wood Sheet Machine where a series of nine sheets are formed continuously, pressed and dried. The white water which has drained into a holding tank is recirculated through the sheet-making machine during the formation of the nine sheets. The sheets are then reduced to ash at 1700 F. for 2 hours and the percent ash remaining is measured. Sheets 3, 5, '7 and 9 are then averaged to give a consistent picture of the percent ash remaining. Of course, the higher the ash total, the great-er the retention ability of the additive. The retention aid is added to the pulp furnish containing the titania and alum in any amount as desired, and sheets are made by the same method as in the above blank runs.

Various copolymers were prepared according to the general polymerization techniques outlined above. The ratio of monomers was varied in order to determine those specific polymers giving highest retention activity, as determined by a Phototester determination. Table I below outlines retention testing of various samples in which the composition of the polymer was varied as indicated as well as dosage levels and pH of the pulp furnish.

Table I above illustrates the fact that the monomer ratios of the two components going to make up the copolymers of the invention can be varied over a considerable range with no substantial loss of retention activity.

Next a total of 42 samples of a 5% concentrated solution of a copolymer comprising acrylamide and diallyamine in a 3:1 ratio were tested for retention activity as measured by the Phototester method. Dosages were varied from 0.2 to 3.2 pounds per ton and the pH of the pulp furnish was adjusted at either 4.5, 5.5, or 7.4. Phototester values ranges from 15.8 to 37.5.

Next, a series of samples were synthesized in order to determine whether increase in molecular weight, as determined by viscosity measurements, has a tendency to increase the efiectiveness of the polymeric products as retention aids. In this study, samples were prepared in which the molecular weight was varied according to certain manipulative variations of the general polymerization techniques as outlined above. The monomer ratio was kept constant in all cases at 3:1 of acrylamide to diallylamine as well as dosage level of 1.6 lbs/ton and pH of pulp furnish at 5.5.

TABLE II Viscosity centipoises (5% solids): Phototester factor 2,700 31.5 11,000 37.0 25,000 38.0

It can be readily seen that the effectiveness of the polymers as retention aids is in direct correlation to their molecular weight, with the most eficient polymers having the highest viscosity. These results become more meaningful when they are converted to percent retention by multiplying each figure by a factor of ten. Thus, use of one of the retention aids of the invention increases the retention of inorganic fillers from 315% to 380% as shown in Table II. Also, it is seen that higher molecular weight products give a substantial increase up to 20% or more in filler retention over the relatively low molecular weight materials although both types show good effectiveness. This type of comparison becomes more striking when speaking in terms of tons of filler which can be utilized by using the retention polymers of the invention. A considerable savings per Week or per month becomes quite evident when considered in this manner.

Samples were also prepared and tested in which the copolymer content was varied from 5% concentration in liquid solution to a completely solid active copolymer. In all cases excellent retention activity was noted.

Also, ash determinations of sheets prepared while using the retention aids of the invention showed from tested for their retention activity. In all cases, retention ability was of many magnitudes less. For, example, polyacrylamide samples gave Phototester number average results from to 5. Also, polymerized diallyl'a-mine salt gave substantially no retention activity.

The retention aids may be added at almost any step in' the normal mill process but it is greatly preferred they be, added subsequent to the refining step. The most pre-.

ferred site of addition is at the head box. Another practical applicationpoint is at the fan pump where the pulp is simultaneously finally diluted with white water tothe proper consistencyand pumped to the head box. The

retentionaids may also be added after the fiber is beaten and before the refining step, although this is -a less preferred practice, with the effectiveness o'f-the polymers being somewhat .destroyed due to the subsequent agitation and refining steps.

As mentioned above, the polymers of they invention also have activity in improving drainage from the wire surface of the Fourdrinier machine. In many cases, a suitable-retention aid shows little or no activity in improving the drainage of white water from the pulp slurry.

Oftentimes, the converse is also true, that is, effective.

drainage aids exhibit poor retention activity. However, in the case of the instant invention, the copolymeric compositions show excellent activity in both fields of paper treatment. Again, the polymers may be added to the fan pump, head box, wire pit, etc-., prior to actual formation of the paper sheet. It is preferred that when the materials are to be used for this purpose, they be added after the fibers have been refined. The exact mechanism of the drainage improvement is not known, but it is believed that the fiber fines and foreign matter are agglomerated upon the large fiber particles and thereby 'a sufficiently strong fiber mat is produced, which still has sufficient porosity to allow the white water to drain therefrom.

The polymers of the invention have found use in in. creased retention of nearly .all types of inorganic fillers and fiber fines. Particularly their retention action is apparent when such fillers asv naturally occurring organic materials, talc, agalite, pearl filler, barytes and certain clays such as china clay or artificial fillers such as suitably precipitated calcium carbonate, crown filler (pearl hardening) blane fixe, and titanium dioxide pigments are added to the pulp slurry. Inorganic coloring pigments and kaolin clays are also efiiciently retained upon the:

fibers by use of the polymeric substances. As discussed show excellent activity even in the absence of alum.

Through use of the copolymers, excellent retentionof fiber fines and fillers may be realized in both 'Fourdrinier and cylinder paper machine systems. Increased filler retention realized from the use of these compounds results in a brighter sheet with better density, opacity, and ashcontent. Also better sheet formation, smoothness, printability and porosity, and greatly reduced two-sidedness, that is, differences of such properties as color and brightening of the respective sheet sides due to uneven pigment retention, are noted when these copolymers are employed. In addition to the above advantages, use :of the retention agent results in cleaner machine operation and a less abrasive system, reduced load to thesaveall,

alized through the use of the copolymers-was a decrease in pinholes in the .paper sheetwith a resultant improved paper product.

The invention is hereby claimed as follows:

1. A method of improving the retention of inorganic.

filler and fiber fines in the processing of paper which comprises the step of adding to an aqueous filled paper, pulp suspension at least a retention improving dosage of an organic water-soluble copolymer formed as the reaction product of 50-95' parts by weight of acrylamide and 550 parts by weight of a polymerizable compound selected from the group consisting of- 'diallylamine and -'salts t thereof.

2. A method of improving'theretention of inorganic filler and fiber fines in the processing'ofpapenwhich' comprises the step :of addingto an aqueous 'filled paper pulp suspension at least 0.01 pound per ton of fiber of an organic water-soluble polymer formed as" the reactionproduct of 50 parts by weightof acrylamide and 5 50' parts. by weigh t of a polymerizable .compound selected from the group consisting of 'diallylamine and salts thereof.

3. The .method of claim 2 wherein the filled paper pulp suspemsionalso contains an aluminum salt.=

4. -The method ofclaim 3 wherein-the aluminum; salt is alum.

5. A method of improving the retention of an inorganic filler and fiber fines in the processing of paper which 5 comprises the step of ad.ding to an aqueous filled paper pulp suspension containing alum at least 0.1 pound per ton offiber of an organic :water-soluble copolymer formed as the reaction product. of 500-9510 parts by weightv of acrylamide and 50-500 parts'by .weightof a polymerizableidiallyl amine selected from .the group consisting of the free base and salt thereof.

6. The method of claim 5 wherein said diallyla'mine has the following structural formula:

' of hydrogengand methyl radicalstand R is a memberofa class consisting of hydrogen and lower alkyl radicals.

7.'A method of improving the drainage properties of aqueous paper pulp sheet which comprises the steps of treating an aqueous paper pulp suspension with'at least 0.01 pound perton of fiber of an organic, water-soluble copolymer-formed as the reaction-productof=50-95 parts,

by weight of an acryla'rnide and 5-50 parts by'weight of a polymerizable compound selectedfrom the group consisting ofdiallylamine and salts thereof;:depositing such treated aqueous pulp suspension ,upon a foraminous forming surface to form a continuous aqueous paper sheet comprising water and a paper fiber; network, and drain-' ingsaidwater from said fiber network,

8. The-method of claim 7 wherein the aqueous paper pulp suspension also contains alum.

References Cited by the Examiner DONALLH. svLvnsrnnrl-imar Examiner.

MORRIS O; WOLK, Examiner. 

1. A METHOD OF IMPROVING THE RETENTION OF INORGANIC FILLER AND FIBER FINES IN THE PROCESSING OF PAPER WHICH COMPRISES THE STEP OF ADDING TO AN AQUEOUS FILLED PAPER PULP SUSPENSION AT LEAST A RETENTION IMPROVING DOSAGE OF AN ORGANIC WATER-SOLUBLE COPOLYMER FORMED AS THE REACTION PRODUCT OF 50-95 PARTS BY WEIGHT OF ACRYLAMIDE AND 5-50 PARTS BY WEIGHT OF A POLYMERIZABLE COMPOUND SELECTED FROM THE GROUP CONSISTING OF DIALLYLAMINE AND SALTS THEREOF. 